1. Field of Invention
The present invention relates to the field of material handling and carts.
2. Description of Prior Art
Many improvements have been made in the field of carts and dollies. The present inventor, Dahl, in U.S. Pat. No. 5,228,716, teaches a cart with foldable sides and a telescoping frame adapted to accommodate numerous shapes and sizes of cargo. Dahl's first carts utilized relatively small diameter swivel casters with solid wheels that were problematic for users who needed to traverse grass or dirt, particularly with heavy loads. Many professional film crews and sound crews require carts that would feature 4 pneumatic wheels to roll heavy equipment over rough terrain, such as grass football fields, that nonetheless will fold to a small storage size for easy transport in SUVs or airlines. Because all known 4-wheeled carts featuring pneumatic wheels are extremely heavy and bulky, they are not functional in terms of folding to a small storage size for use in smaller vehicles or airlines, where sheer bulk of the carts displace valuable space needed for equipment storage. Furthermore, airlines have recently raised rates for extra cargo, making lower weight and size of traveling equipment crucial. In addition to the need of pneumatic wheel units mounted on a foldable cart, video and sound crews often require a shelf that would attach quickly to the cart in the field in order to support camera, video, or sound equipment. The inventor set about creating a collapsible cart and expandable shelf system that would remedy these concerns.
Others have realized the usefulness of pneumatic wheels on carts, however, they have failed to solve the problems of weight, transportability, or to effectively eliminate caster “shudder” or “chatter” while a cart is rolling. U.S. Pat. No. 3,785,669 to Doheny teaches a convertible cart that is often used by video professionals who have sometimes replaced the original 5″ swivel casters with pneumatic swivel casters. However, this cart is extremely heavy, bulky, and does not fold down with the pneumatic casters attached. In addition, the frame fails to retract in length making the storage size unsuitable for SUV's, etc. U.S. Pat. No. 4,009,891 teaches a convertible cart that does not fold small for storage, is extremely heavy, and does not feature pneumatic casters which would require extensive redesigning of the frame. Regarding technology relating to a cart shelf to support camera, video or sound equipment, others have attempted such an improvement, but have not done so in a manner that teaches the limitations of the present invention. For instance, U.S. Pat. No. 5,536,034 to Miller teaches a convertible bulk hand truck and tabletop, however, this is essentially a table mounted to Doheny's cart. Unfortunately, the Miller technology as configured was too bulky and heavy when transporting in a vehicle or airline. The present invention is materially different in form and function. Other wheeled devices and table combinations are shown in U.S. Pat. Nos. 4,284,286, 4,565,382, 5,004,263; 5,160,182; 5,201,536, however, none of these patents have configurations and functional capability of serving as a two wheeled dolly and four wheeled cart while also including features that serve to convert the four wheeled cart into a portable work table.
Because of the substantial demands of film and video crews for extremely collapsible carts to carry extremely heavy loads over rough terrain, the present invention typically employs four 8-10″ diameter pneumatic wheel units on the inventor's collapsible cart. Although such pneumatic wheel units are naturally lighter than solid tire counterparts, the inherent diameter of the wheel still presents a significant challenge in terms of portability and weight. These factors contributed to the genesis of the invention of this cart model. Obstacles included but were not limited to oversized and excessively heavy mounting plates on commercially available caster and wheel units that could not be utilized without significantly interfering with the functionality of the cart. Typical pneumatic plate casters were far too heavy (exceeding 7-8 pounds each), which when used in the inventor's 2-wheel handtruck configuration caused the inventor's previous carts to become top-heavy and topple over. The frame design used by the inventor on the entire frame design weighed less than 25 pounds without the casters, so this excessive weight was unacceptable. U.S. Pat. No. 3,283,358 to Merriam teaches such a common plate caster, however, this design is extremely heavy, and tended to interfere with the operation of the inventor's cart. Typical plate casters with pneumatic wheels were not usable because the width of the mounting plates (typically 4″×4.5″ diameter) would strike against the frame components and interfere with the folding handle operation of the cart. In addition, mounting the steel plate to the square tube front axel of the inventor's cart was cumbersome, heavy, bulky, and negated many of the design goals of the inventor. The bulky caster mounting plate would constantly snag on items during storage/transport and would require significant widening of the front axel, a feature further discussed herein. During the inventive process, and in researching available caster and wheel technologies, the inventor found that existing units featured bulky bearing caps that would interfere with operation and the release mechanisms of the foldable handles. Although pneumatic stem (post) casters are available, they too were also found too heavy and bulky to allow the inventor's cart to function correctly. Because of weight, they also would cause the cart to topple over when used in upright 2-wheel handtruck position (one of the inventor's cart's foldable positions). For instance, U.S. Pat. No. 4,709,444 to Black teaches a stem caster wheel unit secured by pins, but this caster is not removable and the stem is solid which added too much weight. In addition, the horn assembly of Black weighted too much if enlarged to accommodate an 8″ diameter pneumatic wheel. U.S. Pat. No. 164,226 to Sheldon teaches a stem furniture caster that has no way of securing the stem inside the furniture to accommodate constant removal and if the article was to be constantly lifted off of the ground. Similarly, U.S. Pat. No. 4,969,230 to Huang and U.S. Pat. No. 4,707,880 to Doyle teach removable stem casters, however the solid stem was also determined too heavy for application with inventor's cart. U.S. Pat. No. 4,224,714 to Salpos discloses a caster essentially designed for use with wood furniture, which is unsuitable. U.S. Pat. No. 6,810,561 to Liu teaches a ring stem caster with a threaded bolt that would be far too heavy when enlarged to accommodate 8″ diameter pneumatic tires. For these reasons, the inventor developed a novel wheel and caster unit with a small bearing cap and modified tube stem extending therefrom.
Another major problem addressed by this invention is that pneumatic swivel casters tend to shudder excessively when mounted on a cart with a lightweight frame. This “chatter” or “shudder” (side-to-side wobbling) is very undesirable when transporting delicate and expensive photo, video, or musical equipment (or any other cargo) and greatly reduces the cart's functionality. This problem is also compounded because large rubber pneumatic tires have a tendency while rolling to stick slightly or grab on hard surfaces such as concrete. The lighter the cart frame, the more pronounced are such problems. The combination of the inventor's lightweight frame (approximately 25 lb.) and the large diameter of the pneumatic casters (8-10″ diameter), created excessive caster chatter when installed on inventor's cart frame. This chatter would render inventor's cart unusable as a viable equipment mover. The inventor attempted to solve the problem with commercially available technologies-to no avail. U.S. Pat. No. 5,809,612 to Finch teaches an anti-shimming caster wheel, however, it is functionally different than this inventor's solution. Finch's technology was also heavy and not an economically viable alternative for use with the present invention. U.S. Pat. No. 4,097,954 to Christiansen teaches a flutter-resistant caster that would cause premature bearing wear when used with a caster featuring 8″ or larger diameter wheels and heavy loads. In addition, the plate mount was undesirable because of weight and bulk.
In addition, inventor's frame needed to be significantly redesigned to accommodate this caster and still meet the original design goals of the cart in terms of small storage size, expandable frame, stability and steady transport. Early in the design process, research determined that the cart would topple over when making sharp turns with pneumatic casters installed in the same position as smaller casters on previous carts. To maintain turn stability and maintain a small storage size, further research revealed a preferable width of a front axle on the frame of the cart of at least eighteen inches in width. The inventor's cart had the front axel modified accordingly to accommodate this new type of caster and to prevent toppling of the cart when the cart made sharp turns. The pneumatic swivel casters were therefore positioned farther apart on the front axel than the smaller casters on previous carts.
To further transform inventor's cart into a field workstation while meeting Dahl's original design goals, a new type of shelf system was designed which featured light weight, fast set-up, and small storage size for transport when removed from the cart. In addition, this shelf could change length that could be mirrored by altering the length of the inventor's telescoping cart. This feature is extremely advantageous in situations when space was at a premium in the field, using a small equipment set-up, or navigating the labyrinth hallways in auditoriums, hotels, etc. The shelf was attached to the cart via holes in the foldable handles and using wingbolts and wingnuts. U-shaped brackets welded to the steel shelf support tubes fit over the vertical cart handles providing a rigid shelf platform when the wingbolts were tightened.